1. Field of Invention
This invention relates to methods and diagnostic kits for detecting the cellular membrane magnesium binding defect, which deficiency is critically associated with certain abnormal physiological states, e.g. sodium-sensitive essential hypertension and type 2 insulin-resistant diabetes mellitus.
2. Description of the Prior Art
Elevated arterial pressure, namely hypertension, is probably among the most important public health problems in developed countries. It is of common occurrence, asymptomatic, readily detectable, and often leads to lethal complications if not treated. Although there are exceptions, most untreated adults with hypertension will continue to experience further increases in their arterial pressure over time. Reports based on actuarial data and clinical experience, estimate that untreated hypertension shortens life by 10 to 20 years. This lower life expectancy is believed to be due to an acceleration of the atherosclerotic process, with the rate of acceleration related in part to the severity of the hypertension. Even individuals with relatively mild diseasexe2x80x94those individuals without evidence of end-organ damagexe2x80x94if left untreated for 7 to 10 years have a high risk of developing significant complications, and more than 50 percent of them will ultimately experience end-organ damage related to hypertension. End organ damage can include cardiomegaly, congestive heart failure, retinopathy, a cerebrovascular accident, and/or renal insufficiency. Thus, even in its mild forms, hypertension can be a lethal disease, if left untreated.
Although awareness of the problems associated with elevated arterial pressure has increased, in 90 to 95 percent of the 60 million, minimally estimated, existing cases in the United States, the cause of the disease, and thus potentially its prevention and cure, is still largely unknown. These individuals have only generalized or functional abnormalities associated with their hypertension and are often diagnosed as having primary, idiopathic or essential hypertension. Several abnormalities have been identified in patients with essential hypertension (see e.g., Meyer P and Marche P, Am. J. Med. Sci. 295: 396-399 (1988)), often with claims, later contested or unsubstantiated, of the abnormalities being primarily responsible for the hypertension. This situation has been attributed generally to the likely possibility that essential hypertension has more than one cause, each of which may be a set of genetically determined, contributory abnormalities, which in turn interact with environmental factors.
The most widely recognized of these possible causes of essential hypertension is sodium, i.e. sodium ion (Na+)sensitivity, also commonly referred to as salt (NaCl)-sensitivity. In such patients hypertension is exacerbated by a high dietary salt intake and diminished by dietary salt restriction. It has been assumed that this abnormality reflects cellular membrane defect, and that this defect occurs in many, perhaps all, cells of the body, particularly the vascular smooth muscle cells. Based on studies using erythrocytes, this defect has been estimated to be present in 35 to 50 percent of the essential hypertension population.
However, Applicant discovered, as disclosed below, the actual complex mechanism underlying sodium-sensitive hypertension, which discovery has yielded a new diagnostic methodology to detect this disease at its early stages.
Type 2 diabetes mellitus is the most common form of diabetes mellitus, comprising 85-90% of the diabetic population and taking heterogeneous forms. Overt diabetes characteristically appears after the age of 40, has a high rate of genetic penetrance unrelated to HLA genes, and is associated with obesity. A strong hereditary component is evident. For example, concordance rates in identical twins is nearly 100 percent.
Among American whites the estimated incidence of Type 2 diabetes mellitus in 1976 was between 1 and 2 percent, but the prevalence has risen as the population has aged and become more obese. More than 10 percent of the older population now suffers from the disease. According to the 1990-1992 National Health Interview Survey, about 625,000 cases of diabetes are diagnosed in the United States each yearxe2x80x94more than 6 times the 1935-36 rate.
Many consider insulin resistance to be the primary cause of Type 2 diabetes mellitus. This pathological state and the consequent hyper-insulinemia develop years before insulin secretion diminishes and overt diabetes mellitus is present. About 20 percent of the white population of the United States has impaired glucose tolerance, i.e. hyperglycemiaxe2x80x94the virtually universally accepted sign of the presence of diabetes mellitus.
Patients affected with overt Type 2 diabetes mellitus retain some endogenous insulin-secreting capacity, but insulin levels in plasma are low relative to the magnitude of insulin resistance and ambient plasma glucose levels. Such patients do not depend on insulin for immediate survival and rarely develop diabetic ketosis.
The clinical presentation of Type 2 diabetes mellitus is insidious. The classical symptoms of diabetes may be mild and tolerated for a long time before the patient seeks medical attention. Moreover, if hyperglycemia is asymptomatic, the disease becomes clinically evident only after complications develop. Such complications include atherosclerosis, the risk for which is greatest in poorly controlled patients. Other sequela of diabetes mellitus are myocardial infarction, stroke, peripheral vascular disease and lower extremity gangrene, neuropathy, nephropathy, diabetic foot syndrome, cardiomyopathy and dermopathy.
Little is known about the specific genetic abnormalities associated with most forms of Type 2 diabetes mellitus. However, applicant has observed the highly frequent occurrence of the magnesium binding defect in the erythrocyte membranes of mildly affected Type 2 diabetics.
Others have found insulin resistance to be caused by what was ostensibly the magnesium binding defect. (See Mattingly MT, Brzezinske WA, Wells IC, Clin. Exper. Hypertensionxe2x80x94Theory and Practice A13: 65-82 (1991).
These observations strongly support the concept that the magnesium binding defect, which is genetic, is the cause of insulin resistance. Therefore, the detection of the presence of this defect in an individual who is asymptomatic would indicate the presence of Type 2 diabetes mellitus in its earliest stage so that management of the disease could begin at the earliest possible time.
This invention involves methods for the detection in humans of physiological disorders, such as sodium-sensitive, essential hypertension and adult onset, Type 2, insulin resistant diabetes mellitus, for which the subnormal binding of magnesium to cellular membranes of the somatic cells is a contributory, critical cause. These methods comprise the quantification of the concentrations, in blood plasma from the above individuals, of the polypeptide degradation products derived from the amidated C-terminal region of the tachykinins such as Substance P. These degradation products are embodied in the amino acid sequence of the pentapeptide which characterizes the amidated, C-terminal amino acid sequences of all of the tachykinins, of mammalian origin, i.e. Phe-X(Phe, Val)-Gly-Leu-Met-NH2.